This dissertation aims to investigate the prosodic development in the canonical babble and first words of infants with cochlear implants (CI) and their normally hearing (NH) peers. Two main research questions are investigated:

When and how do NH infants who start to produce word stress?

When and how do infants with CI start to produce word stress?

These questions are investigated by five studies, with each different methodologies. In total two acoustic studies and three perceptual studies are conducted. These studies take a longitudinal approach, including data from the onset of babbling until a cumulative vocabulary of 200 words was reached, in both NH and CI infants. This range covers the period of the transition from canonical babbling to first words use. Within this range disyllabic babble and early word productions were selected for acoustic (Chapters 2 and 3) and perceptual analysis (Chapters 4, 5 and 6).

When and how do NH infants start to produce word stress? The results show that traces of the predominant trochaic stress pattern are already apparent from babbling onwards. This finding leads to the suggestion that infant babble serves as a training ground for ambient stress production. Moreover, the results show that the advent of first words boosts ambient prosody production. It is concluded that the communicative function of words and the fact that they have a clear adult target leads to refined stress production in typically developing infants.

When and how do infants with CI start to produce word stress? This dissertation uncovers a developmental delay in the production of the fine phonetic detail in CI infants. Children with CI only reach the level of prosodic differentiation in words NH children already display when they are babbling. Given the auditory deprivation and the initial delayed access to speech input, the idea of a developmental delay in prosody production is not surprising: children with CI had less aural exposure than their NH peers and they are still catching up at the time they enter the first word stage. The developmental lag that is already apparent in babbling evolves to an even bigger discrepancy in first word productions. At the time infants with CI start to produce lexical utterances they have had less time to exercise prosody production in canonical babble. This thesis is both clinically and scientifically relevant as it is amongst the first studies to detect such an early developmental delay.